Acquired resistance to ticks was reported in the late l93Os. These findings have been confirmed and extended to guinea pigs and rabbits using several species of ticks by several investigators including ourselves. The proposed project is to identify the molecular basis of the antigens involved in tick immunity and study its effect on the antigens of the B. burgdorferi carried by the ticks and upon the transmission of Lyme borreliosis. Specifically models of tick protective immunity will be established in guinea pigs and in rabbits. Antibodies shown to be capable of passively protecting recipients will be purified using chemical and immunoabsorbent methods. Antigen specificity of lymphocytes from tick protected animals and from clones will be characterized. Tick Salivary and midgut antigens will be obtained from the appropriate organs of Ixodes scapularis and from supernatants and homogenates of tissue cultures; these antigens will be purified by chemical and immunological means. Such antigens will be used to produce tick immunity in the models chosen. With polyclonal and monoclonal antibodies obtained from tick-or purified antigen-sensitized animals DNA libraries will be screened. Such libraries, prepared from stimulated tick salivary glands and midguts, will be used to clone genes encoding protective antigens. Using immune guinea pigs and mice the effect of anti-tick immunity on the surface antigens of tick-borne Borrelia burgdorferi will be studied and the ability of infected ticks to transmit disease to tick-immune host determined. The potential synergistic effects of dual anti-tick and anti- Osp A immunity on the ability of infected ticks to transmit Lyme borreliosis will be investigated in the mouse model.